A steering angle sensor as mentioned above, which serves for determining the steering angle of a rotatably mounted steering element of a motor vehicle, e.g. of a steering wheel or an associated steering shaft, comprises a rotatably mounted drive element which during a rotary movement of the steering element likewise performs a rotary movement, and a rotatably mounted driven element which is in engagement with the drive element and is driven by the same. The steering angle is determined by detecting the rotary movement and/or the angle of rotation of the driven element.
The steering angle sensor for example can serve the determination of the steering angle of a steering wheel of a motor vehicle. For this purpose, the steering angle sensor normally is mounted in the steering column of the motor vehicle and detects e.g. the rotary movement of the steering shaft associated to the steering wheel.
From WO 96/27116 a method and an apparatus for angle measurement of a rotatable body is known, wherein a gear wheel is mounted on the axle of the rotatable body, which is coupled with two further gear wheels and drives the same for rotation. The angles of rotation of the two further gear wheels are measured by means of two periodic angle sensors. The angle sensors are connected with an electronic evaluation circuit which calculates the angle of rotation of the rotatable body.
The measurement accuracy of the steering angle sensor among other things depends on the precision of the toothing. In general, the engagement of the teeth is not without backlash, which is due to the manufacture of the gear wheels. This backlash additionally is increased by mounting tolerances. In addition, the wear of the gear wheels progressing with time plays a role. Furthermore, the inhomogeneity of the shape and the distribution of the teeth as well as non-circular gear wheels are to be noted, which possibly can lead to linearity errors. This backlash of the gear wheels ultimately leads to measurement errors of the steering angle sensor. In the case of a reversal of the direction of rotation of the gear wheel carrying the sensor this error manifests itself as hysteresis error.
As due to these factors the measurement result of the steering angle sensor is subject to error, wherein the error not necessarily is a systematic error, it is desirable to reduce the backlash of the gear wheels, in order to increase the measurement accuracy of the steering angle sensor.
For this purpose, EP 1 132 716 B1 proposes a position sensor as described above, in which the driven gear wheels in addition are pulled or urged radially to the center of the driving gear wheel by means of spring-elastic tension bars. The driven gear wheels are coupled with a movable, more exactly a rotating part of a rotary position sensor, which cooperates with a stationary part of the rotary position sensor, in order to determine the angle of rotation of the rotating part of the rotary position sensor and thus of the steering element. In this device it is disadvantageous that the driven gear wheels and the rotating parts of the rotary position sensors are radially shiftably mounted in a plane which extends orthogonally to the direction of extension of the axes of rotation. Accordingly, the axis of rotation of the movable parts is not stationary with respect to the stationary parts of the rotary position sensor, so that measurement errors are inevitable, even if the engagement of the teeth now is without backlash and mounting tolerances are compensated. At least the wear of the gear wheels progressing with time and the above-mentioned inhomogeneity of the teeth and gear wheels still lead to measurement inaccuracies. The fact that the clamping frame is an additional component which further reduces the anyway confined installation space also represents a disadvantage.